The invention relates to a component and a method for producing the component, in particular it relates to an electronic component with a micro-electronic chip and a carrier.
The method of isothermal coagulation is known for the production of components, particularly the mounting of integrated micro-electronic components on substrates, heat sinks, and the like. A method of this type is described, for example, in German Patent A-195 31 158.
With this method, the micro-electronic components and the heat sink are first coated with metals, wherein at least one metal with low melting point and one metal with higher melting point are used. The metal coatings are brought into direct contact with each other, are heated with a specified temperature progression, and are pressed together during the reaction time, until the reaction between the metal with low melting point and the metal with higher melting point is completed. In the process, the component with low melting point is diffused into the component with higher melting point, thereby resulting in an interconnect layer, which is stable at clearly higher temperatures than the melting temperature for the component with lower melting point. However, the bond is not solid until this isothermal coagulation reaction is completed. For temperatures that can be used with electronic materials, this process can last up to 60 minutes in the range of at most approximately 300xc2x0 C. and is preferably realized in a vacuum furnace. For this, a relatively high pressure must be exerted onto the bonding location during the total time period for joining the two individual parts, thus making it necessary to have a joining process.
Despite the fact that this type of metallic bonding permits a very advantageous thermal coupling per se of a micro-electronic component to a heat sink or heat expander that may exist, the isothermal coagulation method cannot be used in this case because the necessary joining time is several minutes. Thus, this method is not suitable for a commercial production process for micro-electronic components with typical transit times of a few seconds for fitting the chip onto the carrier.
For lowering the total reaction time and thus also the joining time during which the component must be compressed and the interconnect layer coagulates or the reaction is completed, it is suggested that a material combination be selected, which has a higher growth rate for the inter-metallic phase that forms during the isothermal coagulation. A material combination of this type, however, is not suitable for all purposes. According to a further measure to reduce the reaction time, it is suggested that the thickness of the active metal layers be reduced. Cutting the layer thickness in half will reduce the reaction time for many systems to one quarter. However, a lower limit value for the layer thickness reduction is predetermined by the roughness or curvature of the surfaces for the partial elements.
It is the object of the invention to provide a method for producing a component by means of thermal coagulation, as well as to provide a component that requires a joining time of less than one minute.
The above object generally is achieved according to the present invention by a method for producing a component with an interconnect layer between two partial elements, for which: the first contact side of the first partial element is placed onto a second contact side of the second partial element, wherein the first contact side is coated with a first metallic coating and the second contact side is coated with a second metallic coating, and wherein at least one of the metallic coatings is a component with low melting point and at least one of the metallic coatings is a component with higher melting point; the component is heated to a reaction temperature (T1) over a predetermined temperature course and during a reaction period (t1), until an isothermal coagulation reaction between the first and second metallic coating is completed and the interconnect layer has formed; a joining time (t2) starts at the beginning of the reaction period (t1), which joining time is shorter than the reaction time (t1) and that the partial elements are subjected to a static contact pressure during the joining period (t2); at the beginning of the joining period (t2), the two partial elements are subjected, at least during a fraction of the time for the joining period (t2), to vibration energy (P1) in that at least one of the partial elements is put into longitudinal and/or transverse vibrations. Modified embodiments, as well as advantageous embodiments follow from the descriptive section.
The invention starts by dividing the length of the reaction time into two time segments. The first time segment is characterized by the joining period and the second time segment by the remaining reaction time. The actual process of securely joining partial elements to form a single component is carried out during a joining period within the reaction period, in which the isothermal coagulation takes place. The joining period preferably is shorter than the reaction period.
According to the invention, a dynamic contact pressure in the form of vibration energy, particularly ultrasound energy with a predetermined output, is exerted upon the component or the two partial elements during the joining period. Another advantageous manner of introducing vibration energy consists in exerting a frictional vibration upon one or both partial elements, wherein the contact surfaces that are placed against each other are moved against each other, thereby providing mechanical and/or thermal support for the reaction process of the contact surface materials.
It is particularly preferable if the two partial elements are pressed together with a predetermined, static contact pressure, at least at the start of the vibrations or while these vibrations arc effective. It is useful if the contact pressure acts only during the joining period upon the component. It is particularly favorable if the vibration energy and the contact pressure are effective at the same time. The vibration energy preferably should act upon the partial components during a shorter period of time than the length of the joining period. It is particularly preferable if the vibration energy is effective at the start of the joining period.
As a result, the partial elements can be joined mechanically during a very short joining period, such that they have sufficient stability for the further process sequence, as compared to the required actual reaction period while the isothermal coagulation process continues. It is particularly favorable for a production process that the remaining reaction time can be completed at a location other than the joining location where the vibration energy was introduced.
It is advantageous if the time period during which the vibration energy is effective is selected to be shorter if the reaction temperature is selected to be higher.
The time period during which the vibration energy is effective advantageously is between 50 ms and 600 ms. Preferably, the vibration energy should be effective for a period not to exceed 70% of the joining period. The ultrasound output (P1) that is used should advantageously be between 0.3 W/mm2 and 3 W/mm2.
A static contact pressure (F1) of between 0.2 N/mm2 and 1.5 N/mm2 is favorably used; preferred is the use of the highest possible contact pressure. A preferred static contact pressure is at least 1.5 N/mm2 while an advantageous reaction temperature is between 150xc2x0 C. and 400xc2x0 C. A favorable reaction time is between 10 s and 3 minutes.
It is expedient if the method is realized in an inert gas environment, at a temperature that exceeds at least the room temperature.
The first metallic coating should advantageously contain at least one layer of indium, preferably a layer sequence of gold and indium and/or the second metallic coating should contain at least one gold layer and/or one silver layer. It is particularly advantageous if an indium layer at the joining location for both partial elements is brought in contact with a gold layer. Another preferred embodiment provides that two indium layers are deposited, such that they make contact.
It is useful if the metallic coatings are grown on a diffusion barrier layer. A favorable thickness for the diffusion barrier layer is less than 0.5 xcexcm.
A suitable thickness for the first metallic coating is between 3 and 7 xcexcm. The thickness values for the two metallic coatings are adjusted approximately proportional to the inter-metallic phases that form. The thickness of the gold layer should favorably be selected to be approximately half the thickness of the indium layer.
It is particularly advantageous that the indium layer is grown on a thinner layer of gold, which protects an adhesion and barrier layer that may be present.
The first partial element preferably is a micro-electronic chip, particularly a silicon chip, and the second partial element is a heat-conducting body, particularly a silicon body, a ceramic body or a metal body. An interconnect layer of an alloy of AuIn and/or AuIn2 and/or a mixture thereof is positioned between the partial elements.
It is advantageous if the interconnect layer has a diffusion barrier layer to one or both partial elements, particularly a layer of titanium and/or titanium, nickel and chromium. It is particularly advantageous if the interconnect layer is stable at temperatures above 400xc2x0 C.
The features, insofar as they are essential to the invention, are explained in further detail below and with the aid of Figures.